A conventional method of designing an aircraft wing box is described in Multidisciplinary Design Optimization Of A Regional Aircraft Wing Box, G. Schuhmacher et al., AIAA. A simplified Beam Aircraft Model (BAM) is coupled with an aerodynamic panel model to analyze aero-elastic effects. It is also used by a loads group to calculate external loads resulting from flight and ground maneuvers. The loads are partitioned into aerodynamic, inertia and concentrated loads and supplied to a structures group as running loads along the elastic axes of fuselage, wing, control surfaces etc.
A problem with the use of a simplified BAM as in Schuhmacher et al. is that the loads for the control surfaces and wing may not be consistent. That is, the sum of the loads acting on the wing and the control surfaces attached to the wing (flaps, ailerons etc.) may not add up to the total loads acting on the wing.